The present invention relates to a tracer, clamp, and object engager for holding and tracing a lens mount of an eyeglass frame, a lens, and/or a lens pattern, to reliably detect the shape thereof even when the shape includes high wrap. The term "high wrap" as used here in encompasses shapes that have a curvature greater than 6 diopters. Typically, though not necessarily, the high wrap is provided so that the eyeglass frame more closely follows the contour of the wearer's face.
In the eyeglass industry, it desirable to provide lenses having different shapes and sizes to accommodate different sizes and shapes of eyeglass frames. Generally, eyeglass lenses start out as blanks having certain optical properties designed to correct one or more defects in a patient's vision. It is unlikely, however, that every member of the population having such vision defect(s) will agree on one size or shape of eyeglass frame. For this reason, lens blanks are routinely subjected to edge processing in an effort to adapt them to a selected size and shape of eyeglass frames.
This custom edge processing can be achieved using any one of several conventional techniques. According to one such technique, each eyeglass frame manufacturers provide lens patterns that fit within the respective lens mounts of those manufacturers' eyeglass frames. When a patient selects a particular style and size of frame, a lens blank which has been formed to correct that particular patient's vision defect is placed in an edging apparatus along with the pattern or patterns provided by the frame manufacturer. The edging apparatus then traces the pattern and removes material from the periphery of the lens blank in accordance with the pattern. This process is analogous to conventional key duplication techniques. U.S. Pat. No. 5,158,422 to Wagner, assigned to the assignee hereof, discloses an example of such an edging apparatus. Alternatively, the edger may be numerically controlled in order to eliminate the need for patterns.
The conventional pattern-based technique, however, has certain drawbacks associated with it. These drawbacks include, for example, the number of patterns which must be provided, the storage space required for such patterns, and the difficulties which arise when the patterns become misplaced or when they are misaligned during tracing. Typically, one or more patterns must be provided for each different shape and/or size of eyeglass frame. The amount of storage space required for such patterns increases as the choices in eyeglass frame sizes and shapes expand. Therefore, while the conventional technique is generally effective, there remains a need for a more convenient arrangement.
In order to provide a more convenient arrangement, efforts were made to eliminate or reduce the need for patterns by providing a tracing apparatus capable of tracing the lens mounts of eyeglass frames. The results of such tracings then were used to provide edging information for use in edging a lens blank. U.S. Pat. No. 4,724,617 discloses an example of such a tracing apparatus. While such tracing of the frames is generally effective when the lens mounts in the eyeglass frames are substantially planar, problems are frequently encountered when the frames have a high wrap.
In particular, the stylus that performs the tracing in conventional tracers is generally biased in a radially outward direction to engage a groove in the lens opening or mount of the eyeglass frame. This radially outward biasing remains effective so long as the groove in the lens mount extends in the same radially outward direction. Eyeglass frames with high wrap, however, tend to have grooves in the high wrap region which extend obliquely (and which can even approach the perpendicular) with respect to the radially outward direction. There is consequently a tendency for the stylus of the tracing apparatus to "fall out" of the groove as it enters the high wrap region.
This incompatibility between conventional tracers and frames having a high wrap is exacerbated by the effects of gravity when the frames are held in the typical substantially horizontal, downward-facing orientation. In that orientation, the high wrap generally causes the sides of the frames to extend upwardly. As the stylus enters the high wrap region and the groove in the frame gradually transitions to a more upwardly extending orientation, gravity acts to pull the stylus down and out from the groove. The stylus therefore tends to "fall out" of the groove, rendering the tracing completely inaccurate. Tracers which bold the frames in a horizontal, downward-facing orientation therefore tend to be limited to use on substantially planar eyeglass frame configurations.
Eyeglass frames, however, are available in many different shapes and sizes. Recently, eyeglass frames with high wrap shapes have become even more popular than before. There is consequently a need in the art for a versatile eyeglass frame tracer capable of tracing the lens mounts even if the eyeglass frame has a high wrap shape.
There also is a need in the art for a tracer which can trace not only lens mounts with high wrap, but also lens patterns and actual lenses with high wrap when such lens patterns and actual lenses are more readily available to the operator than the eyeglass frames.